I see an important flaw that need addressing on future motherboards RAID controllers (or maybe can be adopted on new drivers for existing chipset).

With the apparition of SSD storage, is possible to pair SSD drives of different speed and capacities.

Nonetheless, all RAID0 controllers distribute data on equal sizes on different storage units. But since SSD speeds are enjoying large improvement in performance, is possible to pair -under RAID- SSD units of different speeds. So it should be possible to store more percentage of data on the faster unit, and get even more speed form the RAID 0.

For example, suppose that SSD1 unit has a speed of 1X, and SSD2 has speed of 2X.

SSD1 is a bottleneck on RAID 0, because SSD2 would write his share of data at 2X speed, and remain half the time idle, waiting for SSD1 to end writing.

The solution would be to write 1/3 of data on SSD1, and 2/3 of data on SSD2, so both units are efficiently used.

The partition on SSD2 should be also 2X larger than the one on SSD1.

That would make the RAID 50% faster than possible on today's solutions.

Is a feature so important that I would choose an chipset over any other solution if it is included. No RAID controller available today has that capacity.

If you're running anything other than RAID0, the way it is is the way it needs to be. A major point of RAID is to enhace reliability so if 1 drive fails you still have all your data, so you can replace the drive and the controller rebuilds the new disk.
For RAID0 though you have a point.